1. Field of the Invention
The present invention relates to a secondary air humidity controller for a melting furnace for manufacturing glass.
2. Discussion of Background
In a melting furnace with a regenerator used for manufacturing glass, flue gas is passed through the regenerator to have heat storage refractory bricks absorbed heat. When the burning direction changes after that, secondary air for combustion is passed through the regenerator at a high temperature to carry out preheating the secondary air and waste heat recovery.
In order to keep the quality of glass articles manufactured by the melting furnace at a high level, the operating conditions of the melting furnace are desired to be stable. There are various factors which are an obstacle to a stable operation and vary the operating conditions of the melting furnace. One of the factors is a change in the temperature (blowing temperature) of the secondary air for combustion which is blown into the melting furnace.
The factor in variation in the blowing temperature has been considered to be a change in the temperature of the atmosphere. The temperature of the secondary air at the inlet of the regenerator changes principally in proportion to the temperature of the atmosphere, resulting in a change in the blowing temperature. There has been known a measure which uses hot air passed through a heat exchanger and controls the mixing rate of the hot air and the atmosphere to regulate the temperature of the secondary air at the inlet of the regenerator at a constant level so as to make the blowing temperature stable in order to prevent the blowing temperature from varying due to a change in the temperature of the atmosphere.
However, the inventors have recently found that a change in the humidity of the atmosphere as well as a change in the temperature of the atmosphere can have effect on the temperature in the melting furnace in some cases. This phenomenon has been found based on discovering that the temperature in the melting furnace goes up when it rains. It is an undesirable phenomenon because of an obstacle to the stable operation of the melting furnace.
The results of thorough investigation showed that the variation in the blowing temperature due to a change in the atmospheric humidity had a range of variation as high as 10.degree. C. in a melting furnace having about 200 t/day of throughput of glass melt, depending on a change in the humidity which varies on a day.
Although the mechanism of the effect which the change in the humidity has on a melting tank is not clear, it is presumed as follows: Beat transfer from the hot refractory bricks to the secondary air for heating the secondary air in the regenerator is carried out mainly by convective heat transfer due to contact. Because most of the heat storage refractory bricks have a high temperature beyond 1000.degree. C., it is presumed that the heat transfer varies as the radiation of steam varies together with the concentration of the steam.
Specifically, it is presumed that a high concentration of H.sub.2 O causes heat transfer from the heat storage refractory bricks to the secondary air due to radiation to increase, and a low concentration of H.sub.2 O causes heat transfer due to radiation to decrease, resulting in a change in the temperature of the secondary air which has passed through the regenerator. Although the atmosphere contains CO.sub.2 as other radiative components, CO.sub.2 can not be one of the factors in variation in the secondary air temperature because CO.sub.2 has small variation unlike steam.